It is well known that water living carnivores, such as salmon, and land based carnivores, such as mink, live under natural conditions, on a diet consisting of 30 to 55% of proteins (90% DS). The choice of food is depending on live phase and specie. A great deal of this protein can be oxidized to form energy providing compounds, such as ATP (adenosine triphosphate), which results in excretion of nitrogen to the environment. At an intense cultivation of e.g. fish and mink this might cause an environmental problem.
During natural conditions omnivores live on a diet consisting of 15 to 30% of proteins (90% DS). During certain conditions this protein might be used for providing energy.
The most energy demanding tissue in the body is the muscles, which obtains its carbohydrate energy from the food directly via the blood or from the liver via the blood in the form of glucose. Glucose is formed in the liver from inter alia decomponents of the proteins of the muscles. The compounds which hereby form glucose are substantially alanine and its corresponding keto acid. It has also been shown that the corresponding keto acids of some essential amino acids, such as alpha keto isocaproate (KIC), may be precursors of amino acids, e.g. KIC of leucine.
(i) NH.sub.4.sup.+ is coupled to amino acids via the reaction NH.sub.4.sup.+ +KG+NADPH=Glutamate+NADP.sup.+ +H.sub.2 O Glutamate provides the alpha amino group in the synthesis of most non-essential amino acids; PA0 (ii) the carbon skeletons present in the synthesis of non-essential amino acids are all intermediates of the glucolysis, the pentose-monophosphate shunt or the citric acid cycle and may hereby be derived from pyruvate or KG (cf FIG. 5) PA0 (iii) at physiological stress, too large energy draft, reproduction conditions and other low energy situations, the oxidation of amino acids increases whereby a deamination with KG or PY as amino receptors belongs to the starting processes (cf. FIG. 6); PA0 (iv) at the synthesis of collagen KG is essential to the hydroxylation of proline. PA0 (i) the formation of lactate to provide the glucolysis with NAD.sup.+ during aerobic conditions; PA0 (ii) formation of acetyl-CoA for the synthesis of fatty acids or digestion in the citric acid cycle; PA0 (iii) a high concentration of acetyl-CoA increases the formation of oxaloacetate, which either provides the citric acid cycle with intermediates (at a low concentration of ATP (adenosine triphosphate) or becomes a substrate in the gluconeogenesis (at high ATP concentrations); PA0 (iv) at the gluconeogenesis pyruvate might possibly contribute to the pentose-monophosphate shunt, where NADPH is formed (essential in several anabolic processes, i.a. the synthesis of the non-essential amino acids) and ribose-5-phosphate, which is a substrate at the synthesis of nucleotides; PA0 (v) the formation of alanine as well as other non-essential amino acids where pyruvate contributes with the carbon skeleton.
Pyruvate is a centre of the metabolism (cf. FIG. 4), where the following steps can be distinguished: